1. Technical Field
The disclosure relates to a gas detector capable of determining presence or absence of sulfur oxides in a predetermined concentration or higher that are contained in exhaust gas (detected gas) of an internal combustion engine or detecting a concentration of sulfur oxides contained in the exhaust gas.
2. Description of Related Art
Conventionally, in order to control an internal combustion engine, an air-fuel ratio sensor (also referred to as an “A/F sensor”) that obtains an air-fuel ratio (A/F) of air mixture in a combustion chamber based on a concentration of oxygen (O2) contained in exhaust gas has widely been used. One type of such an air-fuel ratio sensor is a limiting current type gas sensor.
Furthermore, a SOx concentration detector (hereinafter referred to as a “conventional device”) that detects a concentration of sulfur oxides (hereinafter may also be referred to as “SOx”) in the exhaust gas by using such a limiting current type gas sensor has been proposed (for example, see Japanese Patent Application Publication No. 2015-17931 (JP 2015-17931 A)).
The conventional device includes a sensing cell (an electrochemical cell) that uses an oxygen pumping effect of an oxygen ion conductive solid electrolyte. The conventional device applies a voltage between paired electrodes of the sensing cell to decompose gas components including oxygen atoms in the exhaust gas (for example, O2, SOx, H2O, and the like, and hereinafter also referred to as “oxygen containing components”), and thereby generates oxide ions (O2−). The conventional device detects a characteristic of the current flowing between the electrodes of the sensing cell when the oxide ions, which are generated through decomposition of the oxygen containing components, move between the electrodes (the oxygen pumping effect).
More specifically, the conventional device executes applied voltage sweep when detecting the SOx concentration. That is, the conventional device executes the applied voltage sweep for boosting the applied voltage, which is applied to the sensing cell, from 0.4 V to 0.8 V and then lowering the applied voltage from 0.8 V to 0.4 V.
The conventional device uses a difference between a reference current as the “current flowing between the electrodes of the sensing cell (hereinafter may be referred to as an “electrode current” or an “output current”)” at a time point at which the applied voltage reaches 0.8 V and a peak value as a minimum value of the output current in a period in which the applied voltage is lowered from 0.8 V to 0.4 V, so as to compute the SOx concentration.